1. Field of the Invention
The invention relates to a radiation-sensitive, in particular photosensitive, mixture which contains
(a) a compound having at least one acid-cleavable C--O--C bond, and PA1 (b) a compound which forms a strong acid on exposure to actinic radiation. PA1 (a) a compound having at least one acid-cleavable C--O--C bond and PA1 (b) a compound which forms a strong acid on exposure to actinic radiation. PA1 R.sup.2 is a hydrogen atom or an optionally substituted alkyl radical containing 1 to 4 carbon atoms, PA1 R.sup.3 is an n-valent, optionally polymeric aliphatic or aromatic radical and PA1 n is a number from 1 to 100. PA1 (a) exposing the radiation-sensitive mixture described above, and PA1 (b) developing the exposed material.
The invention also relates to methods of forming images using such mixtures and to acid-cleavable compounds useful in such mixtures.
2. Description of Related Art
Positive-working photosensitive mixtures whose exposed areas are more soluble in an aqueous alkaline developer liquid than the unexposed regions are known. In particular, positive-working recording materials based on o-quinone diazides have gained acceptance in practice.
The photosensitivity of these materials is frequently unsatisfactory. An increase in the photosensitivity can be achieved by using catalytically active photosensitive systems since the quantum yield becomes greater than 1 in such systems. Thus, the known principle of initiating secondary reactions by means of photolytically produced acids and thereby inducing an increased solubility of the exposed regions has been used recently for positive-working systems. Under these circumstances, photochemically produced strong acids serve to cleave acid-labile compounds whose cleavage products have a greater solubility in aqueous alkaline developers than the original compounds.
Low-molecular-weight and high-molecular-weight acetals and O,N-acetals containing aromatic compounds as hydroxyl or amino component (see U.S. Pat. No. 3,779,778), and also ortho esters and amide acetals (see DE-C 26 10 842) are used as acid-cleavable compounds. Radiation-sensitive positive-working mixtures are also obtained using polymeric ortho esters (See EP-B 0 022 571) and polymeric aliphatic acetals (See DE-C 27 18 254). Such mixtures are frequently unsatisfactory since the cleavage products obtained by acid-catalyzed fragmentation are often only inadequately soluble in aqueous alkalis and therefore result in problems in the development of such layers. In addition, many of the compounds mentioned can only be obtained with difficulty. In other cases, the storage life of the recording materials concerned is unsatisfactory in the unexposed state.
Polymers containing acid-labile tert-butyl carbonate groupings or tert-butyl carboxylate groupings which function positively in mixtures with photochemical acid donors are described in EP-B 0 102 450 and EP-A 0 366 590. An extrapolation of this principle to molecules having a molecular weight below 500 in combination with conventional binders is to be found in EP-B 0 249 139. Such systems are also not free of disadvantages: the reduced solubility inhibition of the binder matrix compared with o-quinone diazides is manifested in an unduly low resistance of the unexposed regions in the developer (so-called dark erosion) and consequently in a poor differentiation between exposed and unexposed regions.